Biofouling control is an indispensable and intricate part of industrial water treatment because biofouling can cause heat transfer resistance buildup, system pressure increase, corrosion or scale initiation and propagation. In an industrial water system, biofouling includes the formation of a biofilm, i.e., an adherent population of immobile microorganisms on a surface. Biofilms become a source of cell aggregates to the bulk solution through sloughing events which may be triggered by many environmental changes such as temperature, shear, nutrient and biocide additions. Cell aggregates represent a source of microbial inoculation in a system and potential plugging as dispersed aggregates coalesce. The most abundant population of microorganisms in industrial systems is either associated with biofilms or cell aggregates which are sloughed from biofilms. Thus, the goal of biofouling control involves the removal of the existing biofilm, the disinfection of individual cells and cell aggregates, and the prevention of microorganism regrowth in the treated system. Because of the higher density of bacteria and biopolymer inside biofilm and cell aggregates, a much higher concentration of biocide is needed to achieve a desirable result.
The current practice for dealing with microbial fouling in industrial water systems is by the addition of control agents, namely oxidizing and non-oxidizing biocides, to bulk water flow. For the control agents to reach the biofilm, they have to rely on mass transport, i.e., diffusion or convection. Once the agents reach the biofilm, their concentrations are in a very dilute form, so they do not have enough power or persistency to provide adequate disinfection. Therefore, in practice, the majority of biofouling control agents are either wasted by cooling tower stripping, in blowdown or consumed by reactions in the bulk water.
One approach which has been taken to improve biocide delivery for dealing with biofilm growth on surfaces is the encapsulation of biocides used in antifouling coatings. This approach has been implemented in marine applications, such as in U.S. Pat. No. 4,253,877. However, this type of coating approach is impractical for most water systems because once the initial coating has eroded, it is almost impossible to achieve a subsequent coating.
U.S. Pat. No. 4,561,981 discloses the use of microencapsulation and specific gravity to deliver antifouling chemicals for oil production application. Similar approaches have been proposed for papermaking, such as in U.S. Pat. No. 5,164,096. These encapsulation approaches have also been used by the pharmaceutical and agricultural industries quite extensively for controlled release and targeted delivery. Unfortunately, encapsulation has a major drawback in that it is difficult to prepare and the cost is prohibitive for industrial water treatment applications.
U.S. Pat. No. 4,954,338 teaches another approach which utilizes a microemulsion as a biocide carrier. However, the microemulsion is used primarily to solubilize a very low water-soluble active ingredient and not to target a specific surface. Moreover, the active biocide used in the formulation, namely a low water-soluble chlorinated octyl isothiazolone, is more effective as a fungicide and algacide than a microbiocide, so its application has been limited to algae and fungal control.
Emulsions and microemulsions have been used as a way to formulate surfactant and oil-base solvents as cleaners/degreasers, such as in U.S. Pat. Nos. 5,080,831 and 5,585,341. U.S. Pat. No. 5,656,177 makes use of this property and discloses an oil-in-water emulsion free of toxic microbiocides for biofouling prevention, particularly in papermaking processes. However, although this type of emulsion may be effective to some degree for some time, the non-toxic hydrophobic oil is a nutrient for some microorganisms and will eventually promote a selective type of biofouling.
Accordingly, it would be desirable to provide a method of controlling biofouling in aqueous media more efficiently by specifically targeting the treatment chemicals directly to biofilms, cell surfaces and/or cell aggregates in a concentrated form. By targeting the surfaces of interest, more efficient use of antimicrobial treatment chemicals would be made, thereby providing a more environmentally acceptable and economical use of biocides.